A photon is emitted from a source and reflected off an object (or objects) until it hits the human eye. The color of the object we see depends on the photon wavelength. If photon travels with constant speed how does the human eye know how far the object from which the photon was reflected?
[Physics] How does the human eye knows how far the object from which the photon was reflected
geometryphotonsvisible-lightvision
Related Solutions
due to the curvature of the earth, you can only see flat land for about 5km give or take a few hundred meters.
from a sky object you are limited by the photon flux emitted or reflected by that object (50-150 photons in a 1ms burst, and all landing within a 10 arcminute spot on your eye)
the wavelength of those photons affect your sensitivity (green photons are best)
the duration your eyes have spent in darkness (eye sensitivity increases 100 fold by 5th minute in darkness, and 1000x by 15th minute)
apart from 1., all the above information can be found in this famous paper: http://arapaho.nsuok.edu/~salmonto/vs2_lectures/Lecture6.pdf
Let's consider that transparent colored glass, which color wavelength is $\lambda$, It is colored because all the other wavelengths are absorbed and that specific wavelength $\lambda$ gets reflected, In the case when light goes through it, same thing can be observed, all the other wavelengths are absorbed and only that specific $\lambda$ gets through.
For illustration consider the image bellow:
The first filter looks red($\lambda = 700nm$) because all other wavelengths are absorbed and only red is able to go through it or get reflected, Same can be observed with the rest of the filters.
Best Answer
To have depth perception two eyes are needed. Our two eyes are some distance apart which causes the photons from an object to arrive at slightly different angles. The brain then reconstructs the depth field from these differences.
Similarly, we can figure out how far nearby stars are by using images made by a telescope at two different times of the year, since when the earth is (for example) at two opposite positions of its orbit around the sun, it acts like two "eyes" that are a large distance apart.